The May-June 2021 conference was planned for Marseilles, France, but was held online because of the COVID-19 pandemic. The 10 papers in the proceedings examine arithmetic, geometry, cryptography, and coding theory from such perspectives as a strategy to optimize the complexity of Chudnobsky-type algorithms over the projective line, the constant D(q) defined by Homma, arithmetic monodromy groups of dynamical Belyi maps, automorphisms and isogeny graphs of abelian varieties with applications to the superspecial Richelot isogeny graph, and the regulator dominates the rank. Annotation (C)2022 Ringgold, Inc., Portland, OR (protoview.com)